1. Field of the Invention
The present invention is directed generally to a method and apparatus for releasably attaching a closure plate to a casing.
2. Background Information
Munitions which contain explosive or incendiary material are expected to withstand various environmental situations without detonating. These stimuli are associated with hazardous situations that the munition may encounter during its life cycle. If the munition detonates severe property damage and loss of life is possible. Munitions that will not detonate when exposed to these stimuli are known as xe2x80x9cinsensitive munitionsxe2x80x9d.
Munitions may be exposed to elevated temperatures, such as those encountered in a fire, during their life cycle. As the temperature of the material within the munition casing increases, the material expands and the pressure increases. At a high enough temperature and pressure the material will spontaneously combust and, if the pressure is allowed to increase further, detonate.
Munitions may also be exposed to severe localized shocks caused by ammunition, fragments from detonating munitions or from the shock wave of a nearby detonating munition. These shocks cause a localized rapid temperature and pressure increase in the material within the munition casing. As this temperature and pressure increase and propagate through the material the munition detonates.
Munitions are also often required to withstand general severe shock loads (e.g. 50,000 times the acceleration due to gravity on Earth (Gs), or lesser or greater) and still operate. As an example, penetrating warheads are designed to penetrate hard targets such as bunkers or armor without failure of the case or premature detonation.
One method for rendering munitions insensitive was stress risers, which are areas of reduced casing thickness. Stress risers have been designed so a casing will rapidly fail at a stress riser when the pressure within the casing reaches a predetermined level, lower than the pressure at which the explosive material will detonate. Because stress risers weaken the casing, they can cause the casing to fail during shock loads, such as those encountered when a munition strikes a hard target.
Some safety devices rely on venting the warhead casing when the internal pressure reaches a certain level. For example, U.S. Pat. No. 4,423,683, Telmo et al., illustrates an enclosure plate for a warhead which is designed to fail when the internal pressure reaches a predetermined value.
Other safety devices are activated by a rise in ambient temperature near the warhead. U.S. Pat. No. 4,084,512, San Miguel, illustrates a case venting system which employs thermally conductive plugs for preferentially conducting ambient heat to burn fuel located inside the casing near thin points of the casing. The fuel burns though the casing and vents the casing before the explosive material can detonate. U.S. Pat. Nos. 5,786,544 and 5,813,219, both to Gill et al., use a venting device and pyrotechnic pellets which ignite at a desired temperature to non-explosively burn the propellant within the rocket motor of a warhead. U.S. Pat. No. 5,466,537, Diede et al., illustrates an intermetallic thermal sensor for use in venting or mitigation systems.
Some designs incorporate materials which melt at a desired ambient temperature. U.S. Pat. Nos. 5,311,820 and 5,735,114, Ellingsen, provide an interface between a case and closure or nozzle which is designed to release at a temperature lower than the auto-ignition temperature of the propellant contained within a rocket motor. U.S. Pat. Nos. 5,394,803, and 5,398,498, both to Mort, illustrate joint constructions for use between a rocket motor and a warhead which separate when subjected to high temperatures. U.S. Pat. No. 5,155,298, to Koontz, illustrates another safety apparatus for venting a warhead in high temperature environments, which uses a eutectic solder to hold a snap ring in place. All the references in the above paragraphs are incorporated herein by reference in their entireties.
Systems which incorporate materials which melt at a desired ambient temperature typically have numerous complex parts, resulting in high production costs and complex assembly methods. Further, these designs generally lack strength sufficient to withstand shock loads encountered by penetrating warheads during impact. In addition, these systems typically require significant redesign of current warhead casings.
Accordingly, it is an object of the invention to provide an apparatus which releases pressure within a warhead casing when exposed to a heat source, and which can withstand shock loads.
Exemplary embodiments of the present invention are directed to providing an apparatus for releasably attaching a closure plate to an open end of a cylindrical casing, comprising an inner member; a threaded outer ring biased in tension, disposed adjacent to the inner member, for releasably engaging an interior wall of the casing; and a eutectic spacer between the inner member and the outer ring.
Exemplary embodiments of the invention are also directed to a method for assembling an apparatus for releasably attaching a closure plate to a casing, with a inner member sized to fit within a hollow cylindrical casing, the inner member having a groove formed on an outer peripheral surface of the inner member, and an outer ring sized to fit within the groove of the inner member, the outer ring having two ends and a threaded outer peripheral surface. The method includes: positioning the outer ring in an expanded position partially within the groove of the inner member; and forming a eutectic spacer in an annular space defined by a surface of the outer ring in an expanded position and a surface of the inner member by filling the annular space with a liquid eutectic material, and cooling the liquid eutectic material to form a solid eutectic spacer while the outer ring is held in an expanded position.
Exemplary embodiments of the invention are also directed to a method for releasably attaching a closure plate to a casing with an apparatus having an inner member, an externally threaded outer ring biased in tension, disposed adjacent to the inner member for releasably engaging an interior wall of the casing, a eutectic spacer between the inner member and the outer ring, and bleed means for releasing the eutectic spacer when in a melted state. The method includes fitting the closure plate within an opening in an open end of a cylindrical casing so the closure plate abuts an internal surface of the cylindrical casing; and threading the apparatus into the cylindrical casing so the external threads of the outer ring engage internal threads of the cylindrical casing, wherein the apparatus holds the closure place in contact with the casing.